Numbers 35:30

“He who strikes a man so that he dies shall surely be put to death.

“But if he did not lie in wait for him, but God let him fall into his hand, then I will appoint you a place to which he may flee.

‘If a man strikes down the life of any human being, he shall surely be put to death.

“On the mouth of two witnesses or three witnesses, he who is to die shall be put to death; he shall not be put to death on the mouth of one witness.

“Now this is the case of the manslayer who may flee there and live: when he strikes down his friend without premeditation, not hating him previously—

“A single witness shall not rise up against a man on account of any iniquity or any sin which he has committed; at the mouth of two or three witnesses a matter shall be established.

‘Cursed is he who strikes his neighbor in secret.’ And all the people shall say, ‘Amen.’

“Speak to the sons of Israel, saying, ‘Designate the cities of refuge, of which I spoke to you by the hand of Moses,

These were the appointed cities for all the sons of Israel and for the sojourner who sojourns among them, that whoever strikes down any person unintentionally may flee there and not die by the hand of the avenger of blood until he stands before the congregation.